Abstract

We present spectral energy distribution modelling of 6875 stars in
omega Centauri, obtaining stellar luminosities and temperatures by
fitting literature photometry to state-of-the-art MARCS stellar models.
By comparison to four different sets of isochrones, we provide a new
distance estimate to the cluster of 4850 +/- 200 (random error) +/- 120
(systematic error) pc, a reddening of E(B - V) = 0.08 +/- 0.02 (random)
+/- 0.02 (systematic) mag and a differential reddening of DeltaE(B -
V) < 0.02 mag for an age of 12 Gyr. Several new post-early-AGB
candidates are also found. Infrared excesses of stars were used to
measure total mass-loss rates for individual stars down to ~7 ×
10-8Msolar yr-1. We find a total dust
mass-loss rate from the cluster of 1.3 +/-0.80.5
× 10-9Msolaryr-1, with the total
gas mass-loss rate being > 1.2 +/- 0.60.5
× 10-6Msolaryr-1. Half of the
cluster's dust production and 30 per cent of its gas production comes
from the two most extreme stars - V6 and V42 - for which we present new
Gemini/T-ReCS mid-infrared spectroscopy, possibly showing that V42 has
carbon-rich dust. The cluster's dust temperatures are found to be
typically >~550 K. Mass-loss apparently does not vary significantly
with metallicity within the cluster, but shows some correlation with
barium enhancement, which appears to occur in cooler stars, and
especially on the anomalous RGB. Limits to outflow velocities,
dust-to-gas ratios for the dusty objects and the possibility of
short-time-scale mass-loss variability are also discussed in the context
of mass-loss from low-metallicity stars. The ubiquity of dust around
stars near the RGB tip suggests significant dusty mass-loss on the RGB;
we estimate that typically 0.20-0.25Msolar of mass-loss
occurs on the RGB. From observational limits on intracluster material,
we suggest the dust is being cleared on a time-scale of
<~105 yr.